At the age of 16 he began studying architecture in the office of George Snell, a prominent Boston architect.

In 1861 Fehmer was associated with architects Gridley James Fox Bryant and Arthur Gilman, at least to the extent of producing their presentation drawing of their 1862-65 Boston City Hall, one of the first Second Empire buildings in the country.

[2] During the Civil War, Fehmer served in the militia at Fort Independence as a member of the "New England Guards" Fourth Battalion under Major Thomas Stevenson.

The plan included a drawing room with furnishings and decorations by the Herter Brothers dating to 1883, the last of that firm's great commissions.

[3][4] A later account ("Costliest in the City") describes Ames and Fehmer decorating it with a summer buying trip through Europe.